Classified abstracts 2835-2887

Classified abstracts 2 8 3 5 - 2 8 8 7 Classified abstracts 2835-2842 on this page.

Editor's note

The label immediately foflowing the title of each item denotes country of origin of publication, and at the end of each abstract indicates country of origin of work (where known).

I. G e n e r a l v a c u u m engineering

s c i e n c e and

11. GASES AND SOLIDS II 2835. Effect of hydrogen on the temperature dependence of the elastic constants of tantalum single crystals. (USA) An investigation was undertaken to determine whether or not a significant Snoek relaxation mechanism exists when hydrogen is dissolved in tantalum. The experimental approach involved the determination of the changes in the absolute values and the tentperature (in the range 136-298 K) dependence of the elastic constants of single crystals charged with varying amounts of hydrogen up to 10.3 at. %. Changes in the absolute values of the elastic constants, as a function of hydrogen concentration, were found to be linear, with positive slopes for C~ t, CL, and C ~ , and a negative slope for C'. The/small negative slope of C' yields the distortion parameter (Az - ,~2) value of 0.0274. The bulk modult,s and the Voight average Young's modult,s were found to increase when hydrogen was introduced into the crystal lattice. The elastic constants exhibit no change in their temperature dependence when either the temperature (in the range 245-298 K) or the hydrogen concentration (in the range 0-10.3 at. %) was varied. It is concluded that a Snoek relaxation attributed to tetrahedral symmetry of the locally distorted tantalum cubic lattice by hydrogen is insignificant. W L S Stewart et al, J Appl Phys, 48 (I), 1977, 75-81. II 2836. Field emission from oxidized niobium electrodes at 295 and 4.2 K. (GB) Among the various methods proposed to reduce the electron field emission in Nb superconducting cavities, we have investigated oxidization and compared the pc field emission current front bare Nb plane surfaces with that from oxidized ones. The thickness of the NbzO5 layer (from 0 to 160 nm), temperature (normal and superconducting states) and previous electronic bombardment were considered. Experiments show that threshold and breakdown D¢ voltages increase with the thickness of the oxide layer up to 160 nm. The improvement seems to be independent of the temperature and of previous electronic bombardment. (France) G J Sayag et al, J Phys E: Scient hsstrum, 10 (2), 1977, 176-179. I1 2837. S o m e comments on electron-beam-induced adsorption. (GB) Measurements are reported which demonstrate that an ion beam of significant intensity can be generated by an electron gun of the type commonly used in Auger electron spectroscopy. When adsorption experiments are performed in the presence of an electron beam, the ion beam produced simultaneously can significantly influence adsorption behaviour. As an example, the effect is illustrated for the GaAs-O2 system. J H Neave and B A Joyce, J P h y s D: ApplPhys, 10 (2), 1977, 243-248. 11 2838. Defects in silicon substrates. (USA) This paper reviews some defects of major importance in silicon substrates : their nature and geometrical distribution ; the mechanism of formation; their interplays; and their implications. Topics discussed include swirl aggregates of point-defect clusters and dislocation clusters; dislocations generated by thermal stresses; stacking faults generated by thermal oxidation both on the surface and in the bulk of substrates; and clustering and precipitation of oxygen. S M Hu, J Vac Sci Technol, 14 (1), 1977, 17-31.

I1

2839. Shrinkage and annihilation of stacking faults in silicon. (USA) Shrinkage and annihilation of oxidation-induced stacking faults in silicon have been investigated by means of combined methods of successive annealing in nitrogen atmosphere and etching technique. The shrinkage rates were measured and the activation energies for shrinkage were determined to be 4.1 and 4.9 eV for (l I l) and (100) surfaces, respectively. Experimental results are interpreted in terms of climbing of a Frank loop, indicating that the shrinkage process is governed by a mechanism in connection with the self-diffusion of silicon. A novel gettering technique is proposed. (Japan) Y Sugita et aI, J Fac Sci Technol, 14 (1), 1977, 44 46. II 2840. Application of silicates to the detection of flaws in glassy passivation films deposited on silicon substrates. (USA) Silicates have been found to etch extrinsic silicon in a manner similar to hydroxides of alkali metals. Chemically simpler forms of silicates are strongly basic in nature and possess anisotropic properties when applied to Si masked by a defective glassy film. That is, they distinguish among the crystallographic planes in monocrystalline silicon. More complex forms of silicates, waterglasses in particular, do not show these properties. Because of the preferential character of silicon etching, the silicates pinpoint discontinuities in glassy passiration films. These etchants are applicable to n- and p-type silicon in a wide range of resistivities. The advantage which the investigated silicates have over hydroxides of alkali metals is that they etch the glasses at considerably lower rates, which makes them suitable for destructive characterization of very thin passivation films. I J Pugacz-Muraszkiewicz and B R Hammond, J Vac Sci Technol, 14 (l), 1977, 49-53. 11 2841. Effect of vacuum ambience on AI-Si contacts. (USA) Aluminium-silicon contacts are extensively used in integrated circuits. Contact resistance of AI-Si contacts is sensitive to silicon surface preparation, vacuum ambience of aluminium film deposition, and contact sintering conditions. Controlled contamination experiments have been carried out using HzO, 02, and CO during the aluminium film deposition to evaluate the effect on the AI-Si contact resistance. A known gas was admitted to the vacuum chamber by a controlled leak valve and the partial pressure of the gas was monitored with a UTI 100 C quadruple mass analyzer. The substrates consisted of n-type (l 1 I) silicon slices completely processed through boron base and phosphorus emitter diffusions. Al-Si contacts were sintered in the 400-550°C temperature range in Nz ambience. Al surfaces and AI-Si interfaces were Auger characterized. These results along with the contact resistance data (determined with an appropriate test structure) have been examined and it is concluded that gaseous contaminants such as HzO, Oz, and CO in the vacuum chamber up to partial pressures of 5 × 10 -7 tort (6.7 x 10 -5 Pa) do not adversely affect the aluminium silicon interface contact resistance. J C Blair and P B Ghate, J Vac Sci Technol, 14 (1), 1977, 79-84. II 2842. Tunnel MIS solar cells. (USA) In a recent publication we have proposed an explanation for the operation of Schottky-barrier solar cells with an interfacial oxide layer based on the concept that they are minority-carrier nonequilibrium MIS tunnel diodes. Such devices represent a potentially lowcost method for fabricating large-scale solar-energy-conversion arrays both with single crystals and polycrystalline film semiconductors. These solar cells are identical to the conventional p - n junction device except for the location of the depletion region. Our 495

Classified abstracts 2 8 4 3 - 2 8 5 2 calculations indicate that one would have to grow defect-free ultrathin (10-15 ,~ in the case of AI-SiO_,-Si structure) interracial oxide layers to get highest conversion efficiencies from these devices. Performance of tunnel MIS solar cells will be described with main emphasis on the role of surface states and oxide charges. (Canada) R Singh and J Shcwchun, J Vac Sci Technol, 14 (I), 1977, 89-91. 12. GASEOUS ELECTRONICS 12 2843. Positive column of Na-Ne-Ar ac discharges. (USA) The positive column of 50-Hz ac discharges in a mixture of sodium vapor and noble gas (99 vol ~o Ne-I vol ,"o Ar) has been investigated experimentally. The experimental conditions werc as follows: discharge tube radius 10 ram, noble-gas pressure 5.5 torr at 20 C, and sodium density (2.4 - 5.7) ;- l0 ~9 m -a which corresponds to a tube wall temperature of 519 - 538 K. The r.m.s, values of the current ranged from 0.25 to 1.5 A. The discharge propcrties, measured with the aid of electrostatic probes, show hysteresis effects especially for high r.m.s, current values. This behavior can be explained from the combined effects of depletion of sodium atoms and diffusion. It is found that the experimental data on the timeresolved electron temperature agree with calculated values. Qualitative agreement is obtained between the measured and calculated data on the electron density, electric field strength, and radiated power. (Netherlands) T G Verbeek and H V Tongeren, J ,4ppl Phys, 48 (2), 1977, 577-580. 12 2844. Ionization, attachment and negative ion reactions in carbon dioxide. (GB) From measurements of the relative abundances of O - and CO3ions produced in carbon dioxide by electron attachment and subsequent ion-molecule reactions, and from current-growth data, values of the primary ionization coefficient, attachment coefficient and rate coefficient for the reaction O - -F 2CO,--+ CO3- -: CO2 have been obtained for 60 >: 10 - ' 7 ~-: E/N .4 152 :. 10 -17 V c m 2 at gas number densities N between 0.2 and 5.0 :.: l0 in cm -~. S R Alger and J A Rees, J Phys D: Appl Phys, 9 (161, 1976, 2359-2367. 12 2845. Micro-particle detection in an electrically stressed vacuum gap. (GB) It has been postulated that micro-particles (1-100 t~m diameter) can lead to the breakdown of an electrically stressed gap and this possibility has been demonstrated by artificially introduced particles. However, there is very little direct evidence of particles being involved in the breakdown process between practical vacuum-insulated electrodes. This paper describes an attempt to detect such particles in transit and to correlate them with electrical breakdown. The technique used was to arrange for any particles to traverse a system of fringes formed by the interference of two laser beams and detect the scattered light with a photomultiplier. Single particles above 5 tzm can be detected. No particles were observed in a variety of gaps between 0.5 and 2 mm stressed at up to 200 MV m - t whether or not subsequent breakdown occurred. If particles in this range do exist the field required to detach them is apparently greater than that which the gap will withstand before breakdown occurs by other mechanisms. J Smalley, JPhys D: ApplPhys, 9 (161, 1976, 2397-2401. 12 2846. Components of cathode erosion in vacuum ares. (GB) The composition of cathode mass loss was analysed for cadmium, copper and molybdenum vacuum arcs. It showed that two dominant flows are present, one consisting of ions, the other of molten droplets which have sizes in the order of microns to tens of microns. The droplet flow is mainly oriented along the cathode plane and is strongly dependent on the fusion temperature of the cathode metal and the charge transfer by the arc. The cathode mass loss in vapour form is considered to be small. (Netherlands) J E Daalder, JPhys D: ApplPhys, 9 (16), 1976, 2379-2395. 12 2847. Apparatus for measuring the force of gravity on freely falling electrons. (USA) An apparatus and data analysis technique for measuring the gravitational force on freely falling electrons are described. The measure-

496

mcnt required that all I\nrces acting on thc clcctrons bc unilk~rm and measurable to about 10- ~ eV/m. The electrical force along the axis of the 5-cm-dia, vertical copper tube used in the experiment was found to be about 6 ,: 10 ~ cV/m =~ 9 ' { o w h c n t h e t u b e w a s c o o l c d to 4.2 K. Forces on electrons due to magnetic field gradients were reduced well below the electrical ones by selecting only ground state electrons for measurement. Othcr forces were reduced sullicicntly by careful attention to the vacuunl and thcrmal environment. The absence, at 4.2 K, of much stronger electric fields, which were expected to arise from the patch effect and from differential lattice components, contrasts strongly with measttrements of electric fields near metal surfaces made at room temperature. F C Witteborn and W M Fairbank, Rer Sci Instrum. 48 111. 1977, I-I I. 12

2848. Mercury-cesium vacuum-uv laser using charge-exchange pumping. (USA) A mercury-ccsiunl laser using the charge-exchange pumf}ing mechanism is analyzed. The particle and photon rate equations are solved analytically and numerically, and peak laser intensity of order 100 W/cm 2 at 1849 A. is calculated. J F Seely, J ,4ppl Phys, 48 (I), 1977, 263-266. 12 2849. H20, NO, and N:O infrared lasers pumped directly and indirectly by electronic-vibrational energy transfer. (USA) Pulsed infrared molecular lasers are reported in which pumping is via electronic-vibrational energy transfer from Br(42P,/.,). H20 and NO lasers are pumped directly by E-V transfer and operate on a variety of transitions not previously seen in stimulated emission. The N20 laser operates near 10.9 ~m and is pumped by a two-step process involving E - V transfer to an intermediate molecule and subsequent V-V transfer from that molecule to N:O. This latter technique extends the applicability of E - V pumping to molecules which do not interact directly with the electronically excited species. A B Petersen el al, J ,4ppIPhys, 48 (I), 1977, 230-233. 12 2850. A continuous HF chemical laser: production of fluorine atoms by a microwave discharge. (USA) We have used a slow-wave structure to dissociate SF6 and obtain the fluorine atoms for a cw hydrogen fluoride chemical laser. The laser output power has been observed to increase linearly with the absorbed microwave power. The effect of rare gases in the mixture is discussed. It is shown that the laser power increases linearly with their ionization potentials. Those features indicate that electron collisions are essential for the generation of fluorine atoms. In this respect, contributions involving metastable atoms are negligible. No simple relation is observed between the intensity of the fluorine spectral lines in the discharge and the laser power. (Canada) L Bertrand et al, J Appl Phys, 48 (I), 1977, 224-229. 12 2851. Cataphoretic distributions of Co, Ni and Mn in melalhalide-He discharges. (USA) Longitudinal emission intensity measurements for the metals Co, Ni and Mn in the gas phase in a positive column He discharge tube, where the source of the metal is the corresponding metal chloride contained in a conventional appendage reservoir, have been made. The conditions of the discharge were similar to those of a typical metal vapor laser and concentrations of these nonvolatile metals achieved which are comparable to the positive column lasers. The longitudinal dependence of the CI + and various metal atom concentrations illustrates that they are strongly bound together by chemical recombination occurring on the wall of the bore. The failure of such a system to maintain Cu in any appreciable concentration illustrates its limits of applicability, but investigations of laser action in numerous new metal vapor systems should be possible. L A Cross and L L Funk, JApplPhys, 48 (11, 1977, 94-98. 12 2852. Work function and secondary emission studies of various Cu crystal faces. (USA) The work function and its temperature dependence has been measured for the < 1 0 0 > , < 1 1 0 > , < 1 1 1 > , < 1 1 2 > as well as 13 other Cu crystal planes. The results, obtained with two types of incident electron beam techniques in this experiment, are in good agreement with recent photoelectric and contact potential difference results reported on ion-sputter-cleaned surfaces. Variation in secondary emission for different crystal results reported on ion-

Classified abstracts 2 8 5 3 - 2 8 5 8

sputter-cleaned surfaces. Variation in secondary emission for different crystal faces was found to bc determined primarily by the work function changes of tile different crystals and not so much by the bulk lattice orientation. It was also observed that tile secondary electrons are not as dependent on the velocity constraints imposed by, the Bragg condition as are the electrons having thermal energies. G A Haas and R E Thomas, J ,4ppl Phys, 48 ( I ), 1977. 86-93.

gas plasma results in the growth of a carbon rich layer o f tmusual structure and properties. (GB) L Holhmd, J I "oc Sci Techmd. 14 (I), 1977, 5-15.

II. V a c u u m

a p p a r a t u s and auxiliaries

12 2853. Source for negative halogen ions. (USA) A simple and inexpensive ion source has been developed for collision dynamic studies. The negative halogen ions are produced by negative surface ionization at a hot surface of LaB~,. Because of the selectivity of this ionization process mass selection is not necessary. Emission densities of 10-'* A/cm 2 at an energy spread of 0.55 eV are obtained. N Kashihira el al, Rer Sci Instrtml, 48 (2), 1977, 171-172. 12 2854. The correlation of changes of work-function with changes of phase of the erbium hydrogen system. (G B) The effects of hydrogen on the work-function of erbium films at 295 K have been correlated with the various phases of hydrogenerbium system. The erbium films were evaporated from high-purity metal on to glass substrates in uHv. The changes of work-function were studied by following the change of contact potential difference between the lilm and a gold reference surface. The phase changes of the system were deduced from changes in the electrical resistance of the films. For the = phase of the system, small doses of H., reduced the work-function ~b to 0.I eV below the value fro for the clean metal, but larger doses increased to 0.17 eV above ,~o. Further doses Hz took the system into the mixed phase (= -~ /3) in which ff quickly rose to a maximum of 0.53 eV above ~o and then remained constant throughout the rest of this phase, and the ,8 phase. When the mixed phase (,8 + "r) was reached, there was a rapid decrease of ff to at least 0.4 eV below ,~o. The results for the = phase can be interpreted as changes of surface potential; but the results for the other phases depend on changes of the Fermi level of the H/Er system as well as on the surface potential. J Miiller and N A Surplice, J Phys D: ,4ppl Phys, 10 (2), 1977, 213-223. 12 2855. Some characteristics and uses of low pressure plasmas in materials science. (USA) (Welch Memorial Lecture) The preparation of stable thin films of controlled structure, composition and thickness is a discipline bridging vacuum and materials sciences which has had significant effect on optics and electronics, although providing a limited number of working thin-film substances. Techniques continue to be studied to extend the range of usable film materials on which thin-film devices often depend for their development. Increasing use has been made in thin-film technology of physical and chemical phenomena occurring in low-pressure plasmas which are convenient in situ sources of activated gas and energetic ions to be applied as additional agents in film growth mechanisms. Thus ion extraction from plasmas for uniform doping during film growth is more likely to find wide use than ion implantation of solids. Energetic ions and/or activated species in ionized gas are now employed in processes for stoface treatment (nitriding), deposition (sputtering, 'ion plating,' activated evaporation, plasma polymerization), and also for etching (sputtering, plasma etching). Although processes exist in which both physical and chemical effects are recognized to occur, treatment of the process mechanisms tends to be divided between two schools--one concerned with physical effects such as ion impact sputtering and implantation, and the other with chemical effects arising from the release of reactive species in plasma-activated gases. Experiments are described which show that the inner walls of a plasma reaction vessel acquire in the electrode region a negative potential to the plasma in excess of the floating value related to the random electron energy. Ions and electrons are accelerated in the positive ion sheaths which form at the walls of the vessel confining the plasma. Some recent experiments are described which demonstrate how reactive and energetic plasma components can interact. These studies show that (i) gaseous reaction products are more rapidly released from carbon in an Oz plasma by ion impact, (ii) prevention of polymer growth on a surface by sputtering in a fluorocarbon gas plasma exposes the surface to more rapid attack by fluorine radicals, and (iii) energetic ion bombardment of degraded material during deposition on a target in a hydrocarbon

22. PUMPS AND PUIVlP FLUIDS 22 2856. The calibration of vacuum gauges. (GB) This review covers the different techniques that are available for the calibration of vacuum gauges, dealing with both calibration by comparison with an absolute gauge and calibration on a primary standard which generates known low pressures. The various sources of systematic uncertainty in both the series expansion and the orifice flow methods are examined and quantified. The performances of some calibration systems are compared. Parts of this review also cover the possible use of fixed points in vacuum metrology, reference gauges and the intercomparison of standards between laboratories. K F Poulter, J Phys E: Scient htstrum. 10 (2), 1977, 112-125.

III. V a c u u m

applications

30. EVAPORATION AND DEPOSITION IN VACUO 30 2857. Role of structural defects in electron transport properties of copper films. (USA) Kinetics of annealing of tile electrical resistivity p, Hall coefficient R,, mobility tL and thermoelectric power TEP of thin (160-5000 A) copper films deposited at temperatures ranging from 80 to 600 K have been studied. The activation energy for the associated recovery process has been obtained from the observed isothermal and isochronal changes in the resistance of the flms. This energy increases from a value of 0.7 eV at 2000 A, to 1.4 eV at 180 A, for room-temperature-deposited Cu films. Changes in p, R,, and ~. on annealing are found to decrease with film thickness and deposition and annealing temperatures. On the other hand, changes in TEP due to annealing increase with film thickness up to 3000 A; the rate of change depends sensitively on deposition temperature. With decreasing temperature of deposition, the reduction in TEP occurs at successively higher annealing temperature. Annealing does not affect the temperature dependence of Rn and TEP. These results, together with the information on the microstructure of the films and the known sacttering behavior of structural defects in the bulk, lead us to conclude that (l) the reduction in p, RH and/z on annealing is due to the annihilation of vacancies; (2) the corresponding changes in TEP are due to the decrease in the concentration of vacancies as well as the density of dislocations. Quantitative effects of vacancies and dislocations on RH and TEP have been deduced from the observed data. The enormously large contributions of the defects may be understood qualitatively in terms of the variations in the density of holelike states and/or the energy dependence of conductivity (at the Fermi surface), caused by changes in the extent and/or degree of curvature of the necks at the Fermi surface. (India) K L Chopra et al, J Appl Phys, 48 (2), 1977, 538-546. 3O 2858. Magnetic anisotropy in evaporated amorphous films of the ternary system Gd~(FE~_yCoy)l_x. (USA) Magnetic anisotropy has been determined for evaporated amorphous films of Gd~,(Fel_yCoy)l_~, with 0.08 < x < 0.35 and 0.06 < y < 0.62. The anisotropy data were fitted with a dipolar equation of the form K, = ~ Cy Mt M~ in which Cl~ is a dipolar coupling constant for the i-j pair and M~ and Mj are sublattice magnetizations. The model satisfactorily described the experimental data for all films that were amorphous. The anisotropy could be attributed to pair ordering in which rare earth-transition metal pairs (G-Co and Gd-Fe) contribute to in-plane anisotropy and rare earth-rare earth (Gd-Gd) and transition metal-transition metal (Fe-Fe, C o - C o and Fe--Co) pairs contribute to perpendicular anisotropy. The F e - C o pairs were the strongest contributor to perpendicular anisotropy with CFc.-.= = 2.809,

CF=-v= =

0.992 and Cc,-c, = 0.660.

R C Taylor and A Gangulee, J Appl Phys, 48 (1), 1977, 358-361.

497

Classified abstracts 2859-2868

30 2859. Effects of electron-beam radiation on MOS structures as influenced by the silicon dopant. (USA) The flatband shift induced by 25-keV electron-beam radiation in unbiased MOS structures depends in great part on the type and concentration of the dopant in the silicon. The flatband shifts for n-type samples are less pronounced than those for p-type samples. and in general are in the opposite direction. The radiation-induced interface states, however, are independent of the dopant. The difference between the flatband shifts is shown to be best explained by a model based on the assumption that the interface states above midgap are acceptor-type states, and those below are donor-type states. A quantitative analysis made with this model indicates that the radiation-induced fixed oxide charge also is independent of the dopant. The dopant dependence of the flatband shifts can thus be attributed entirely to the charging effects of the interface states. By use of the same model, the apparent discrepancy between the shifts in the threshold voltage and in the flatband voltage of a MOSFET can also be readily resolved. A simple midgap method is implemented to obtain the fixed oxide charge without using interface-state information; the results agree well with those obtained by the more conventional flatband method, which must take the interface-state effects into account. G A Scoggan and T P Ma, J Appl Phys, 48 ( I ). 1977, 294 300. 30 2860. Voltage readout of a temperature-controlled thin film thickness monitor. (GB) A temperature-controlled crystal oscillator installed in a vacuum chamber can be stabilized to within - 0.05°C at a preset temperature. The frequency shift of the oscillator due to film deposition is detected by a digital mixer implemented by application of AND and NOR gates and is then converted to a voltage by a transistor-diode pump. A linear dependence of voltage readout on film thickness to within 1 ~ of linearity can be obtained. (Taiwan) J T Lue, J Phys E: Scient hlstrum, 10 (2), 1977, 161-163. 30 2861. Crystallization of amorphous Si films formed by chemical vapor deposition. (USA) The crystallization process of chemically vapor deposited (CVD) amorphous Si films was studied by using a differential scanning calorimeter. A sharp exothermic peak due to amorphous-polycrystalline transition was obtained in the 665-700~C range. The crystallization temperature was determined to be 665~C. Transmission-electron diffraction and transmission-electron microscopic examinations revealed that, when amorphous Si film is heated at a slightly higher temperature than the crystallization temperature, the Si dendrite grains nucleate, and grow in size with heating time. (Japan) N Nagasuma and N Kubota, J Vac Sci Technol, 14 (1), 1977. 54-56. 30 2862. Heterojunctions in photovoltaic devices. (USA) Heterojunctions have interesting optical properties which make them attractive for solar cells. Several types of heterostructure solar cells have been investigated: heteroface, abrupt heterojunction and graded-gap heterojunction solar cells. The primary advantage of heterostructure cells is the enhanced short-wavelength response although there is potential for low-cost cells with polycrystalline material. The improvement in solar-cell performance for heterojunctions depends upon the selection of semiconductors with useful energy gaps that are closely matched in lattice-spacing and thermalexpansion coefficients. The importance of the heterojunction interface and its dependence on material properties is discussed. Various fabrication methods are discussed and their application to the different types of heterostructures. Recent performance data for material systems representative of each type of heterostructure cell are discussed and considered in terms of maximum expected performance. D L Feucht, J Vac Sci Technol, 14 (1), 1977, 57-64. 30 2863. Growth and characterization of thin-film compound semiconductor photovoltaic heterojunctions. (USA) The fabrication and characteristics of several vacuum-deposited photovoltaic heterojunctions involving ternary compounds (CuInSe,, CulnS2 and CuInTez) and a binary compound (InP) with Cds are described. The light and dark I V characteristics, spectral response 498

data, and cell parameters (fill factors, open-circuit voltages, shortcircuit currents, efficiencies) are reported for the thin-film solar cells. !. L Kazmershi et al, J Voc Sci Techm,I, 14 ( I ), 1977, 65-68. 3O 2864. Rate controlling and composition analysis of alloy deposition processes by electron impact emission spectroscopy (EIES). (USA) The technique of electron-impact emission spectroscopy (EIES) has been used to monitor and control the alloy deposition process. The multicomponent evaporant flux is allowed to pass through a sensor where is it excited by electron bombardment. Narrow-band optical filters are employed to select the specilic emission line or lines from each component. At a specific electron-excitation energy, the emission intensity of the characteric spectral lines from any constituent is proportional to the number density of that constituent in the vapor flux. Experimental results on an aluminiunl-copper alloy system indicate that this technique has sufficient sensitivity and selectivity for most alloy deposition processes. EIES also offers several advantages over other existing monitoring techniques. C Lu et al, J Vac Sci Technol. 14 (I), 1977, 103 107. 31. SPUTTERING 31 2865. Composition, structure, and ac conductivity of if-sputtered calcia-stabilized zirconia thin films. (USA) Thin 12 mole 0~, calcia-stabilized zirconia CSZ films (500-17,000/~) were deposited by rf sputtering onto single-crystal silicon substrates. When deposited in an oxygen-containing plasma (more than 0.2 ~ 02 in Kr), sucb films appeared to be stoicbiometric, as verified by nuclear microanalysis; while their structure, analyzed by x-rays, appeared to be of the fluorite type. The ac conductivity measured on AI/CSZ/Si structures between 200 and 400'C suggests an activation energy and a pre-exponential factor close to that of bulk-sintered material having the same composition. This result tends to prove that conductivity in sputtered CSZ thin films is due to anion oxygen movement. Preliminary e.m.f, measurement on Pt/O,./CSZ/Ni/Si thin-film galvanic cells confirmed this interpretation. (France) M Croset et al, J / I p p l Phys, 48 (2), 1977, 775-780. 31 2866. The angular variation of the sputter yield peak for silica glass targets. (USA) A relation based on ion reflection at a surface atom plane is shown to be capable of predicting the angular position of the maxima of the sputter-yield curve for silica glass targets under bombardment by ions in the energy range 3-50 keV for 19 different ion-ion energy combinations. (South Africa) M J Witcomb, J Appl Phys, 48 ( I ), 1977,434-436. 31 2867. Optical properties of cosputtered gold-chromium alloy films. (USA) Optical properties of cosputtered thin-film (1500 /~) polycrystalline Au-Cr alloys have been investigated in the energy range 0.2-6.1 eV. Cosputtering of Au and Cr has extended the solubility limits of Cr in Au from 20 to 48 at. °/0 .The reflectance data were analyzed by the Kramers-Kronig method and presented in terms of intraband and interband contributions. The observed frequency dependence of the relaxation time is explained on the basis of a two carrier mode. The shift in the Fermi level with increasing Cr concentration is found to be closer to the prediction of the Friedel theory than the rigid band model. The character of critical points for the interband transitions has been identified. W Slusark et al, J Appl Phys, 48 (I), 1977, 248-255. 31 2868. Extremely high stress in graded interracial layers: thin films of H f on sapphire. (USA) A rf sputtering technique is described which makes possible the formation of a very gradually graded interracial layer between a substrate and a deposited thin film. In our experiments with Hf on AIzO3, the gradual transition from AltO3 through mixed phases to Hf was graded over a distance of ,-~340 A. Stress was measured in films deposited over such graded layers, on films without graded layers, and on the graded layer itself. It was found that the graded interfacial layer had a very high stress concentration (1-2 x I0 t° dynes/cm 2, compressive). The residual stress in films deposited without the graded interracial layer was influenced mainly by rfinduced substrate bias during deposition. Films deposited at zero

Classified abstracts 2869-2878 bias with high deposition target voltages exhibited acceptably lowstress levels (5 • 10s dynes/era-') to produce very high bond strength of the film to the substrate as determined by a severe gouging test. .I L Vosscn et al, J I'uc Sci Techm)l, 14 (I), 1977, 85-88. 31 2869. The r.f. glow discharge sputtering model. (USA) A model of rf sputtering systems is qualitatively described. The model allows simulation of an entire system so that tile deposition process can be related to externally measured parameters. The steps in deriving the model are outlined, with some key equations and underlying assumptions given. The model is based on the physical processes that occur in the chamber, such as ionization, sputtering and material transport. This model relates these processes to electrical-circuit parameters and to resultant film-deposition conditions. Theory and experiment are compared for a system at 40 MHz to show reasonable agreement with the model. As an example of use of the model, the effects of phase and rcemission on secondary electron energy are calculated, showing that the damaging effects of highenergy electrons incident on the substrate can be minimized by use of zero-phase and high reemission levels. J S Logan et al, J Vac Sci Technol. 14 (I), 1977, 92-97. 31 2870. Copper/oxygen glow discharge spectrometry. (USA) The reactive sputtering of copper in an oxygen/neon rf discharge has been studied using glow discharge mass spectrometry (GDS). Ionized molecular species incident on the substrate table were monitored during sputter deposition of films onto silicon substrates. Films were prepared over an oxygen pressure range that exhibited significant variations in GDS signal levels. These films were characterized by AES, XPS, XRD and electron microprobe. Good correlalation was found between tilm composition and GDS signal levels. A .I Purdes et aI, J Vac Sci Technol, 14 (I), 1977, 98-101. 31 2871. Vacuum technologies applied to electronic component fabrication. (USA) The application of rf diode sputtering, evaporation, and plasmaetching processes is linding an important role in the manufacture of such components as surface-wave devices, masks, electroluminescent displays and magnetic-bubble elements. Descriptions are given of the critical control required when using rf sputtering and evaporation techniques in order to produce components with required characteristics. The use of in sittt resistance monitoring during deposition processes for layers of resistance from I~/i-! to 5MrS/C? is also included. The change in device and component characteristics with variations in process control prameters will be described. (GB) J E Curran, J Vuc Sci Technol, 14 (1), 1977, 108-113. 31 2872. Early growth of thin films deposited by ion-beam sputtering. (USA) The early growth of sputtered thin films of silver/graphite, silver/ mica, silver/silicon, gold/silicon, and silicon/graphite have been studied using the itt situ electron-microscope technique. Silver nuclei (20-100 ,~) deposited on graphite substrates were found to be mobile under the present experimental conditions, but some nuclei can migrate to a distance of several htmdred angstroms. The early growth of silver on air-cleaved muscovite mica was controlled by substratesurface defects. For silver on silicon, a two-layer growth process was observed. The phenomena of nucleus mobility and liquid-like coalescence were not observed during the growth of the first-layer islands. In the cases of silicon on graphite and gold on silicon, the early growth processes were controlled by the substrate-overgrowth chemical interaction. Silicon or gold islands grew in a peculiar way upon an intermediate layer which was either a compound or an alloy of the substrate-overgrowth materials. (Taiwan) Jer-Shen Maa and T E Hutchinson, J Vac Sci Technol, 14 (1), 1977, 116-121. 31 2873. High-rate sputtering of enhanced aluminium mirrors. (USA) Single-layer, high-purity AI films approximately 0.1 ,am thick were made by high-rate planar magnetron sputtering at rates above 12 rim/s-. Reflectance in the visible was found to be at least as high as that reported for carefully made evaporated films. Enhanced reflectors of the standard metal/low/high design were made, with SiO2 as the low-index material and TiO_, the high. The SiOz was rf planar magnetron sputtered from a fused silica target, while the

TiO., ~as formed by reactive dc magnetron sputtering in a 85:15 argon/oxygen mixture. Deposition rates were 2 and 0.38 nm/s, respectively. The visible reflectance of these films was above 95°0 peak and 94",, average. The results of a number of physical and environmental tests on the mirrors are reported. !. D Hartsough and P S Mcl.eod, J I"m. Sci Technol, 14 (I), 1977. 1977, 123 126. 31 2874. Properties of rf-sputtcred AI20~ films deposited by planar magnetron. (USA) In a preliminary study, the following properties of planar magnetron, rf-sputtercd AI203 films were investigated: deposition uniformity, floating substratc bias potential, AI :O ratio and impurity content by tHe+ backscatter analysis, H2 content by proton-proton scattering, microstructure, C-I/ characteristics on Si, dielectric constant and breakdown voltage, resistivity, refractive index, defect density, etch rate, density, intrinsic film stress, step coverage, microhardness, and uv in ir absorption. From this data, it was concluded that these films exhibit potential for use in abrasive or semiconductor chip protection applications. Their use as dielectric passivation, however, is somewhat in doubt under the deposition configuration used in this study. Possible means of film optimization will be discussed. R S Nowicki, J I"~wSci Technol, 14 ( I ), 1977. 127-133.

32. EVACUATION AND SEALING 32 2875. Intense flowing hollow cathode lamp. (USA) An inexpensive, simple, and versatile hollow cathode lamp has been developed which produces intense ion resonance radiation of about I mW into 47r/25 sr. The lamp employs flowing helium gas to sustain the discharge. The construction permits a variety of cathode seed materials to be easily interchanged. The same lamp has been used as a source of ion resonance radiation for Ca, Ba, Zn, Mg, Sr, Yb, and Eu. F H K Rambow and L D Schearer, Rev Sci his/rum, 48 (1), 1977, 92-93. 32 2876. Vacuum ultraviolet radiometry. 3: The argon mini-arc as a new secondary standard of spectral radiance. (USA) A miniature argon arc has been designed and tested as a new transfer standard of spectral radiance for the wavelength range from 114 nm to 330 nm. Calibration has been performed using two primary standard sources: the hydrogen arc from 130 nm to 330 nm and the blackbody line radiation from 114 nm to 130 nm. The mini-arc provides an intense, stable, and reproducible uv continuum with dc power requirements of less than 1.5 kW. The arc characteristics have been investigated, and the sensitivity of the radiant power output to various operating parameters has been measured. The rms uncertainty in the spectral radiance is estimated to be 5.3% above 140 nm and I0.10~ between ll4 and 140 nm, due primarily to uncertainties in the primary standard sources. J M Bridges and W R Orr, Appl Opt, 16 (2), 1977, 367-376. 32 2877. Atomic absorption of thermally dissociated iodine for laser applications. (GB) An absorption cell for the 1.315 rcm iodine laser wavelength has been constructed using thermal dissociation of molecular iodine vapour to produce ground-state iodine atoms. Measurements of the small-signal absorption coefficient for iodine pressures up to 5 torr and temperatures up to 750:C have been compared with the predictions of a simple thermodynamic model of the iodine dissociation equilibrium, and satisfactory agreement obtained. The model readily allows calculation of operating conditions required for the use of the iodine absorber as a saturable absorber, for free-induction decay pulse generation and for coherent pulse propagation experiments. D R Gray et al, JPhys D: Appl Phys, 10 (2), 1977, 169-177. 33. NUCLEONICS 33 2878. Plasma confinement by high-power excitation in a waveguide. (USA) Under TE_,o mode excitation, the electric field in a rectangular waveguide is minimum at the center and has two intensity maxima 499

Classified abstracts 2879-2886 at intermediate points. Consequently, the plasma electrons experience a strong ponderomotive force and are redistributed to assemble around intensity minima. A self-consistent solution of the wave equation for this problem reveals that the plasma density around intensity minima may be enhanced by a factor of 10 for accessible rf power. It also suggests that the electromagnetic waves of frequency less than the plasma frequency a,, can penetrate a dense plasma. In a collisional plasma, the redistribution of electrons is predominantly caused by their inhomogeneous heating by the wave. The confinement in this case may be attained at much lower powers. (India) M S Sodha etaI, JApplPhys, 48 (1). 1977, 110-113. 33 2879. X-ray measurements of electron temperatures in CO2-1aserheated magnetoplasmas. (USA) Electron temperatures of CO,-laser-heated magnetoplasmas were found from differential measurements of soft x-ray continuum through gaseous absorbers. We observed in argon and helium-argon plasmas that T~ increases with longitudinal magnetic field and is a strongly peaked function of the pressure of the target gas. Plasma dynamics are strongly influenced by the presence of at least eighttimes-ionized argon. W Halverson and C V Karmendy, J Appl Phys, 48 (I), 1977, 99-103. 33 2880. Transient response of a cold plasma half-space in the presence of a transverse static magnetic field. (USA) The reflection of a normally incident linearly polarized impulsive plane wave by a cold homogeneous Iossless plasma half-space with a constant magnetic field parallel to the interface is examined. By the use of a perturbation method the expression for the transient reflected field is given in a closed form. Good agreement between the perturbation solution and results computed by the use of the numerical inverse Fourier transform is obtained for the values of the ratio of the electron cyclotron and electron plasma frequency =~ = oJ,/%, less than 0.3. Using the convolution integral, the transient response for the unit step and rectangular incident pulse is given in a closed form. (Yugoslavia) B V Stanic et al, J Appl Phys, 48 (1), 1977, 148-151. 33 2881. Study of electron-beam-produced plasmas by fast photography and emission spectroscopy. (USA) The luminous events produced by a drifting relativistic electron beam (REB) (1-2 MeV, 100 kA, 40 nsec) have been photographed with an image converter of 5-nsec gate time. Coupled with a transmission spectrograph, time-gated snapshots (1 ~sec) of the spectra have been recorded. For air pressure between 0.1 and 0.3 Torr, the beam is self-focused and it yields a spark spectrum containing mainly N +, with some O ÷ and N ÷÷ lines. In 0.8-1 torr of air, the beam is unfocused and it yields the Nz (B -- C) but not the (A -- B) bands. In the presence of a target, the unfocused beam may again produce an air breakdown. A slitless spectrum then yields a two-dimensional image of the event, which may be related to the spatial distribution of the beam. The results are discussed in connection with REB and ion acceleration research. In addition, Lichtenberg-type discharge tracks in a Plexiglas disk irradiated by 2-MeV beams are photographed and compared with the fluorescence lifetime of the N_, (B -- C) bands. P S P Wet et al, J ApplPhys, 48 (2), 1977, 568-576. 34. ELECTRONICS AND HIGH ALTITUDE PHYSICS AND TECHNOLOGY 34 2882. Note on the effects of finite ion mass and electron thermal velocity spread on the aperiodic instabilities of a space-chargeneutralized electron beam in a planar diode. (USA) A hydrodynamic analysis of the aperiodic instabilities of a neutralized drifting electron stream in a short-circuited planar diode is given in this work. The results of this investigation indicate the following: (i) An electron stream can be aperiodically unstable only if the electron stream's Mach number exceeds unity in the diode space. The change from a monoenergetic electron beam to a dispersive electron beam results in a modification of the instability condition, a reduction of the growth rate, and a smaller value of critical current flowing through the diode. (it) The aperiodic instability imbedded in the immobile ion background, i.e., the Pierce instability, cannot be 500

eliminated by the first-order motion of ions. The effect of the linite ion mass is not only to reduce the maximunl growth rate of the Pierce instability and to increase the diode critical current, but also to introduce new aperiodic instabilities with growth rates generally smaller than that of the Pierce instability. (Taiwan) K Yuan, J Appl Phys, 48 ( I ), 1977, 133-135. 36. VACUUM INSTRUMENTATION F O R S U R F A C E S T U D I E S 36 2883. Zn-ion-implantation profiles in CulnSe2 by Auger electron spectroscopy. (USA) The depth distribution of implanted Zn in CulnSe2 was investigated using Auger electron spectroscopy coupled with continuous surface layer removal by argon-ion sputtering. The distribution was found to be influenced by the dose rate used in the implantation. The distribution obtained at a current density of 0.16 ~A/cm 2 is composed of two parts; one having a nearly Gaussian shape in the leading edge and the other having a nearly exponential shape in the trailing edge after the peak concentration. The tail appears to be due to a rapid diffusion process such as interstitial diffusion. A strong diffusion to the surface was observed from the samples implanted with a current density of 2 ~A/cm 2. This out-diffusion may occur through the damaged region as it has a lower activation energy. P W Yu et al, J Appl Phys, 48 (I), 1977, 67-72. 36 2884. Addition of an electron multiplier to the Varian movable Faraday cup assembly for measurement of angular resolved photoemission. (USA) The movable Faraday cup assembly of the varian LEED optics system has been modified by the addition of a channel electron multiplier. Signal-to-noise was increased by several orders of magnitude, rendering the assembly suitable for the measurement of energy distributions of photoelectrons with an angular resolution as small as - 2 . S P Weeks et al, Rer Sci htstrum, 48 (2), 1977, 190-191. 36 2885. New methods for detecting structural defects in glass passivation films. (USA) Conventional test methods to evaluate the quality of glass passivation overcoats on semiconductor devices are generally inadequate and/or destructive. We have recently devised three new methods that overcome these problems: (I) Sequential selective chemical etching of metal/dielectric structures to detect buried, latent, or partial defects as a function of dielectric layer depth. (2) Electrophoretic cell decoration with uv phosphor particles suspended in an insulating liquid, the sample forming one electrode of the cell. (3) Electrostatic corona charging to selectively deposit surface ions from a highvoltage dc discharge on the insulating surfaces of the sample, followed by placing of the charged sample in a suspension of charged carbon black particles in an insulating liquid; depending on the polarity of the ions the particles can be deposited on the insulator surface or at the defect sites. The etching method is most suitable in process research studies, and the electrophoretic technique for demarcating relatively large defects. The corona-decoration method, coupled with automated instrumental readout based on measuring the reflectedlight intensity, is ideal for routine testing of devices because it is fast, simple, sensitive, and nondestructive to devices such as glass-passivated MOS and linear bipolar silicon-integrated circuits. W Kern and R B Comizzoli, J Vac Sci Technol, 14 (1), 1977, 32-39. 36 2886. Role of metallic contamination in the formation of "saucer" pit defects in epitaxial silicon. (USA) Metallic contamination present in silicon wafers prior to epitaxy or introduced during epitaxial processing were found to be responsible for microdefect formation in epitaxial silicon. Such contamination is often due to use of stainless-steel tweezers. The defects as revealed by Secco etching appeared as shallow saucer pits (s-pits). High densities of s-pits were found to affect the surface carrier concentration of the epitaxial layer as measured by the high frequency MOS technique. The s-pits were found to nucleate oxidation-induced stacking faults (OSF) on (100) material during subsequent processing. Neutron activation analysis was used to identify the elements causing s-pits, and transmission electron microscopy analysis was done to

Classified abstract 2887

identify the defect as a dislocation loop. Scveral means of reducing s-pit densities are also presented. C W Pearce and R G NieMabon, J I~w Sci TechmU, 14 (I), 1977, 40-43. 36 2887. Auger investigation of boron-doped SiO,,~Si. (USA) B-doped SiO., grown on Si(100) wafers using standard B.,H~ gas source processing for times varying between 5 and 90 min has bccn investigated with Auger electron spectroscopy. The restllting film consists of ~100-/~ B203 layer on a B-doped SiO2 region separated

fi'om B-doped Si by a Si-B phase. The growth rate of B-doped oxide is considerably faster than dry-O2-grown SiO2. A simple model of oxide growth gives a 6-10-fold increase in solubility and at least a 5-7-fold increase in the effective diffusion coefficient of O in SiO2 in the presence of B. The Si-B phase forms already at short deposition times, reaching a maximum B concentration of (4 ± 2).-: 1022 cm-~. The width of the phase increases and grows into a lamellar structure, with the number and amplitude of lamellae depending on deposition lime. G Moore et al, J l,Tu. Sci Technol, 14 ( 1), 1977, 70-74.

501